This invention relates generally to refiners for removing contaminants from fiber materials, such as recycled or recovered paper and packaging materials. In particular, the present invention relates to refiner stator plates and especially to the outer row of teeth on the stator plates.
Refiner plates are used for imparting mechanical work on fibrous material. Refiner plates having teeth (in contrast to plates having bars) are typically used in refiners which serve to deflake, disperge or mix fibrous materials with or without addition of chemicals. The refiner plates disclosed herein are generally applicable to all toothed plates for dispergers specifically and refiners in general.
Disperging is primarily used in de-inking systems to recover used paper and board for reuse as raw material for producing new paper or board. Disperging is used to detach ink from fiber, disperse and reduce ink and dirt particles to a favorable size for downstream removal, and reduce particles to sizes below visible detection. The disperger is also used to break down stickies, coating particles and wax (collectively referred to as “particles”) that are often in the fibrous material fed to refiner. The particles are removed from the fibers by the disperger become entrained in a suspension of fibrous material and liquid flowing through the refiner, and are removed from the suspension as the particles float or are washed out of the suspension. In addition, the disperger may be used to mechanically treat fibers to retain or improve fiber strength and mix bleaching chemicals with fibrous pulp.
There are typically two types of mechanical dispergers used on recycled fibrous material: kneeders and rotating discs. This disclosure focuses on disc-typed disperger plates that have toothed refiner stator plates. Disc-type dispergers are similar to pulp and chip refiners. A refiner disc typically has mounted thereon an annular plate or an array of plate segments arranged as a circular disc. In a disc-type disperger, pulp is fed to the center of the refiner using a feed screw and moves peripherally through the disperging zone, which is a gap between the rotating (rotor) disk and stationary (stator) disk, and the pulp is ejected from the disperging zone at the periphery of the discs.
The general configuration of a disc-type disperger is two circular discs facing each other with one disc (rotor) being rotated at speeds usually up to 1800 ppm, and potentially higher speeds. The other disc is stationary (stator). Alternatively, both discs may rotate in opposite directions.
On the face of each disc is mounted a plate having teeth (also referred to as pyramids) mounted in tangential rows. A plate may be a single annular plate or an annular array of plate segments. Each row of teeth is typically at a common radius from the center of the disc. The rows of rotor and stator teeth interleave when the rotor and stator discs are opposite each other in the refiner or disperger. The rows of rotor and stator teeth intersect a plane in the disperging zone that is between the discs. Channels are formed between the interleaved rows of teeth. The channels define the disperging zone between the discs.
The fibrous pulp flows alternatively between rotor and stator teeth as the pulp moves through successive rows of rotor and stator teeth. The pulp moves from the center inlet of the disc to a peripheral outlet at the outer circumference of the discs. As fibers pass from rotor teeth to stator teeth and vice-versa, the fibers are impacted as the rows of rotor teeth rotate between rows of stator teeth. The clearance between rotor and stator teeth is typically on the order of 1 to 12 mm (millimeters). The fibers are not cut by the impacts of the teeth, but are severely and alternately flexed. The impacts received by the fiber break the ink and toner particles off of the fiber and into smaller particles, and break the stickie particles off of the fibers.
Two types of plates are commonly used in disc-type dispergers: (1) a pyramidal design (also referred to as a tooth design) having an intermeshing toothed pattern, and (2) a refiner bar design. A novel pyramidal tooth design has been developed for a refiner plate and is disclosed herein.
FIGS. 1a, 1b and 1c show an exemplary pyramidal plate segment having a conventional tooth pattern. An enhanced exemplary pyramidal toothed plate segment is shown in commonly-owned U.S. patent application Publication No. 2005/0194482, entitled “Grooved Pyramid Disperger Plate.” For pyramidal plates, fiber stock is forced radially through small channels created between the teeth on opposite plates, as shown in FIG. 1c. Pulp fibers experience high shear, e.g., impacts, in their passage through dispergers caused by intense fiber-to-fiber and fiber-to-plate friction.
With reference to FIGS. 1a, 1b and 1c, the refiner or disperger 10 comprises disperger plates 14, 15 which are each securable to the face of one of the opposing disperger discs 12, 13. The discs 12, 13, only portions of which are shown in FIG. 1c, each have a center axis 19 about which they rotate, radii 32 and substantially circular peripheries.
A plate may or may not be segmented. A segmented plate is an annular array of plate segments typically mounted on a disperger disc. A non-segmented plate is a one-piece annular plate attached to a disperger disc. Plate segment 14 is for the rotor disc 12 and plate segment 15 is for the stator disc 13. The rotor plate segments 14 are attached to the face of rotor disc 12 in an annular array to form a plate. The segments may be fastened to the disc by any convenient or conventional manner, such as by bolts (not shown) passing through bores 17. The disperger plate segments 14, 15 are arranged side-by-side to form plates attached to the face of the each disc 12, 13.
Each disperger plate segment 14, 15 has an inner edge 22 towards the center 19 of its attached disc and an outer edge 24 near the periphery of its disc. Each plate segment 14, 15 has, on its substrate face concentric rows 26 of pyramids or teeth 28. The rotation of the rotor disc 12 and its plate segments 14 apply a centrifugal force to the refined material, e.g., fibers, that cause the material to move radially outward from the inner edge 22 to the outer edge 24 of the plates. The refined material predominantly move through the disperging zone channels 30 formed between adjacent teeth 28 of the opposing plate segments 14, 15. The refined material flows radially out from the disperging zone into a casing 31 of the refiner 10.
The concentric rows 26 are each at a common radial distance (see radii 32) from the disc center 19 and arranged to intermesh so as to allow the rotor and stator teeth 28 to intersect the plane between the discs. Fiber passing from the center of the stator to the periphery of the discs receive impacts as the rotor teeth 28 pass close to the stator teeth 28. The channel clearance between the rotor teeth 28 and the stator teeth 28 is on the order of 1 to 12 mm so that the fibers are not cut or pinched, but are severely and alternately flexed as they pass in the channels between the teeth on the rotor disc 12 and the teeth on the stator disc 13. Flexing the fiber breaks the ink and toner particles on the fibers into smaller particles and breaks off the stickie particles on the fibers.
FIGS. 2a and 2b show a top view and a side cross-sectional view, respectively, of a standard tooth geometry 34 used in the outer row of a stator plate. The tooth 34 has a pyramidal design consisting of strait sides 36 that taper to the top 38 of the tooth. The sides of the standard tooth 28 are each substantially parallel to a radial 32 of the plate.
A primary role of the disperger plate is to transfer energy pulses (impacts) to the fibers during their passage through the channels between the discs. The widely accepted toothed plate typically includes the square pyramidal tooth geometry with variations in edge length and tooth placement to achieve desired results.
Refiner material passing between the discs can be accelerated to a high velocity due to the centrifugal forces imparted by the rotor disc. Some of the refiner material exits the discs 12, 13 at a high velocity and are flung radially against the refiner casing 31. The high velocity impacts of refiner material against the casing have caused abrasive wear and damaging cavitation to the casing. There is a long felt need for a means to reduce the wear and damage on refiner and disperger casing due and, particularly, to reduce the wear and damage caused by refiner material impacts against the casing.